1. Field of the Invention
The invention relates to determination of layer types of optical disks, and more particularly to determination of layer types of blu-ray disks.
2. Description of the Related Art
An optical disk drive reads/writes data from/into a DVD disk with a laser beam of wavelength about 650 nm, or reads/writes data from/into a BD disk with a laser beam of wavelength about 405 nm. Thus, because optical disks of different types generates laser beam reflection with different wave lengths, when an optical disk is inserted into an optical disk drive, the wave length of the laser beam reflection from the optical disk can be used to determine whether the optical disk is a DVD disk or a BD disk. The wave length of a laser beam used to read./write data from/into the optical disk is therefore determined to be 650 nm corresponding to a DVD disk or 405 nm corresponding to a BD disk.
A multi layer blu-ray disk, BD Intra-Hybrid disc, may comprise multiple layers such as a BD-ROM (read only) layer or a BD-RE/R (rewritable) layer. When the optical disk drive determines an optical disk to be a blu-ray disk, the optical disk drive then determines the number of the layers of the blu-ray disk, and then determines the types of the layers of the blu-ray disk. When the layer of the blu-ray disk is a BD-ROM layer, the optical disk drive must generate a tracking error (TE) signal according to a differential-phase-detection (DPD) result, and then locks a projection trace of a laser beam on a track of the layer according to the tracking error signal. When the layer of the blu-ray disk is a BD-RE layer, the optical disk drive must generate a tracking error signal according to a differential-push-pull (DPP) result, and then lock a projection trace of a laser beam on a track of the layer according to the tracking error signal. If the tracking error signal is not generated according to a method corresponding to the layer type, the optical disk drive cannot lock the projection trace of the laser beam on a track of the layer.
Referring to FIG. 1A, a schematic diagram for generating a tracking error signal according a differential push-pull (DPP) method is shown. An optical disk drive projects a main-beam 100 and two sub-beams 102 and 104 on a track of a BD-RE layer of a blu-ray disk. A groove on the BD-RE layer forms the track. The main-beam 100 is projected on the groove of the track, and the two side-beams 102 and 104 are projected on the two sides of the groove. Four photodetectors respectively detect signal strength of a portion of reflection of the main-beam 100 to obtain signals A, B, C, and D. Two photodetectors detect signal strength of reflection of the sub-beam 102 to obtain signals E and F, and two photodetectors detect signal strength of reflection of the sub-beam 104 to obtain signals G and H. The sum of the signals C and D are then subtracted from the sum of the signals A and B to obtain a signal [(A+B)−(C+D)]. The sum of the signals E and G are then subtracted from the sum of the signals F and H to obtain a signal [(F+H)−(E+G)]. The signals [(A+B)−(C+D)] and [(F+H)−(E+G)] are then added to obtain a tracking error signal of a differential push-pull method.
Referring to FIG. 1B, a schematic diagram for generating a tracking error signal according a differential phase detection (DPD) method is shown. An optical disk drive projects a main-beam 100 on a track of a BD-ROM layer of a blu-ray disk. Data is Pre-recorded on a track on the BDROM layer in a form of a series of pits and lands which correspond to bits 0 and 1. The main-beam 100 is projected on the track, and four photodetectors respectively detect signal strength of a portion of reflection of the main-beam 100 to obtain signals A, B, C, and D. When the main-beam 100 moves along the track, the phases of the signals A, B, C, and D differ from each other, and the optical disk drive derives a tracking error signal from the phase difference between the signals A, B, C, and D according to a differential phase detection method.
When a blu-ray disk is inserted into an optical disk drive, the optical disk drive must first determine the type of the layer of the blu-ray disk, select a method for generating a tracking error signal from a differential phase detection method and a differential push-pull method according to the determined layer type, lock a trace of a laser beam on a track of the layer according to the generated tracking error signal, and then perform a servo calibration process according to reflection of the laser beam from the layer. If the type of the layer is incorrectly determined, the method for generating a tracking error method is also incorrectly selected according based on the wrong layer type, and the tracking error signal cannot be generated. The laser beam therefore cannot be locked on a track of the layer, leading to failure of the servo calibration process. Thus, a method for determining the layer type of a blu-ray disk is therefore required.